1. Field of the Invention
The invention relates to a back light device for a liquid crystal display (LCD), especially to a uniformly lighting direct type back light device and the LCD applying thereof.
2. Description of the Related Art
FIG. 1A is a perspective view showing a typical direct type back light device of a LCD. In FIG. 1A, the typical direct type back light device 10 includes a light guide plate 11, a reflector 12 and a plurality of a plurality of lamps 13, wherein the lamps 13 are disposed between the reflector 12 and the light guide plate 11.
As shown in FIG. 1A, the typical direct type back light device can distribute light from a light source uniformly over the surface of the liquid crystal panel of an LCD. Generally, the shortest distance between the lamps 13 and the plane of the light guide plate 11 can easily produce the best brightness. Further, the brightness will change with the disposition of the lamps 13 on the plane of the light guide plate 11 adjacent to the liquid crystal panel, to produce a bright and dark line change.
To overcome the bright and dark line change, as shown in FIG. 1B, a cross-sectional view of a typical direct type back light device of an LCD is shown. Masking sheets 24 are formed on the plane of the light guide plate 21 adjacent to the liquid crystal panel with respect to the lamps 23 so that the masking sheets 24 can mask light lines. However, this reduces a number of lights passing through the liquid crystal panel and the brightness of the LCD. FIG. 1C is a cross-sectional view showing another typical direct type back light device of an LCD. Regions on a reflector 32 with respect to the lamps 33 are formed to be V-shaped in order to reflect light from the lamps so that the difference between the bright and dark lines on the light guide plate 31 can be reduced. However, this effect is not completed because the reflective lights other than the V-shaped regions still generate the bright and dark line pattern on the plane of the light guide plate adjacent to the liquid crystal panel.